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Analog Delay Chips found in some toy keyboards
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synthmonger



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PostPosted: Sat Jul 07, 2007 5:25 pm    Post subject: Analog Delay Chips found in some toy keyboards Reply with quote  Mark this post and the followings unread

So far I've found analog delay chips in Yamaha's PSS series and Casio MT and MV series keyboards.

I don't have much of a list compiled but these keyboards have them fo' sho.

PSS-470
MT-520
MT-240 (i think)
MV-420-440

They all had something along the lines of "stereo symphonic" feature which leads me to believe that any keyboard from this era and/or brand would have analog delay chips.

I bet there are plenty out there, so crack em' open and find out! Razz



toodles,
-m
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goodrevdoc



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PostPosted: Sat Jul 07, 2007 10:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

What kind of chips? Certainly not Sad1024's or anything. But if there were some MN3204's perhaps, one could indeed construct a very respectable flanger perhaps?
-jsutin
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synthmonger



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PostPosted: Sat Jul 07, 2007 10:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't remember exactly since I haven't touched most for years now. Just recently I modded a pss-470 which has an MN3102 and a MN2306. This is what reminded me of the old ones.

-m
p.s. im drunk sorry if this reply doesn't make sense.
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pdmillar



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PostPosted: Sun Jul 08, 2007 12:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Did you figure anything out about the PSS-470's chorus LFO? The waveform sounds like a trapezoidal wave at about 1 Hz which drives me NUTS. I'm afraid it's probably generated by the CPU although I didn't look at the chorus circuit in detail. I have some MN3207s which might sound interesting if dropped in there.

I'm adding trigger inputs for the awesome FM drum sounds on mine, I'll post details when I get it done.
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synthmonger



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PostPosted: Sun Jul 08, 2007 11:08 am    Post subject: Reply with quote  Mark this post and the followings unread

I looked up the datasheet for the MN3102 clock and just added a pot to make the speed variable. Nothing too crazy. I stuck with a 500k.

I was going to add trig inputs too but I ended up getting bored with it, screwing up all the C keys and just made it a lil noise gizmo with chorus input.

I'd love to see some pics of the trigger inputs you do. It'll make things easier for the next one ;d

Oh you should also google the pss FM chip bending. There are a few sites with some interesting results.
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germaniac



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PostPosted: Tue Jul 10, 2007 12:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Friends,

The Yamaha PSS-460 and PSS-270 also have BBDs, both MN3206, which is 128-stage, 6.4ms max delay. As synthmonger noted, the LFO (at least on the 460/470) is simple analog, so it's possible to add a speed control pot. It would also be possible to disconnect the straight signal from the output and use the BBD output as a sort of variable vibrato. The circuitry associated with the BBD is pretty minimal--a passive low-pass filter on the input and an active low-pass on the output to remove clock noise. There's also an FET gate that's triggered by the keys to chop off noise from the BBD with no signal present. For longer delay or more vibrato warpage you could sub a MN3207 for the MN3206 without any other circuit tweaking needed.

I haven't done any of these mods, but they might be fun. I've often thought about adding built-in analog stuff to one of these little keyboards--a filter, LFO, VCA, distortion. I've been afraid to short something out and destroy to thing
though. . . . Embarassed

Regards,
Joe
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Scott Stites
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PostPosted: Tue Jul 10, 2007 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've purchased a couple of cheap Karaoke machines at garage sales ($1 each). Those each had MN3102/MN3207 pairs. To be honest, those ICs are so easy to get hold of, it probably wasn't even worth the trouble in that case. Joe, remember when we thought we'd hit the goldmine finding those Rat Shack kits? Very Happy

Cheers,
Scott

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germaniac



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PostPosted: Tue Jul 10, 2007 3:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
Joe, remember when we thought we'd hit the goldmine finding those Rat Shack kits? Very Happy

I remember it fondly! It was like, Wow we better snap these up because they're probably the last ones left on earth! That they're not so rare as all that anymore, I guess is sort of a testament to some kind of DIY renaissance we're in the midst of here. Still glad I have those chips though.

But as a matter of fact, the very short delay chips like the MN3206 or MN3209 are still pretty hard to come by. They would seem to be ideal for a vibrato/flanger/comb filter apps. I doubt the PSS keyboard would be much harmed soundwise by harvesting the rare ones and replacing them with commoner 3207s. . . .

BTW, more tidbits about the PSS-460, et al. I just noticed the signal that controls the noise gate on the output of the BBD comes directly from pin 27 of the CPU IC. The signal from this pin is simply marked "SYM" on the schemo I have. I'm assuming this is some kind of gate signal, since it appears to open and close according to key press. If so, is it correct to assume a trigger could be derived from this and used (as well as the gate function itself) for analog control purposes? Anyone know what SYM might mean? Sorry, I guess I'm weaving this thread into a whole other pair of pants--circuit bending.
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pdmillar



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PostPosted: Tue Jul 10, 2007 9:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

If the PSS-460's chorus circuit is at all similar to the 470's, the gate is probably for turning the chorus effect on or off rather than noise-gating. Mine produces a slight fading hiss whenever the chorus is turned on. SYM probably stands for "stereo symphonic."

May I have a look at the schematic? I'm trying to figure out the chorus LFO. I swapped the 3206 for a 3207 in mine, but predictably the amount of pitch-shift in the delayed sound is now unpleasantly high.
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germaniac



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PostPosted: Wed Jul 11, 2007 11:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey PDM,

Yes, IIUC the 460 and 470 are the same except for the color scheme of the case.

I'm afraid you're right about the SYM pin--it simply turns the chorus on and off. I guess I was wishfully thinking. . . .

As for the schemo, the copy I have is large and spread out over four 11x17 pages. I don't have a way to digitize and reconstruct the whole thing, but in the short term, I can take a digital pic of the LFO/BBD section and post it to the forum. In the super short term, it looks like a 68pf cap between pins 5 and 7 on the clock chip determines the delay time. I think a smaller cap, say 1/2 to 1/4 of the size, would make the delay shorter. I can't tell what would decrease the sweep depth, but maybe you can determine that when you see the schemo. OTOH, in the long term, I'd be happy to send you a copy of the whole service manual if you drop me a PM with your address. After that, you're free to post it if you have the means.

Since this thread is going off-topic, how about if I post the LFO/BBD pic in the circuit-bending forum? I'm interested in doing some mods to this thing--I've heard somewhere that there are more options, like two more settings per slider, and control over the vibrato rate and depth, etc.

For the pic, look for a topic in circuit-bending such as "YAMAHA PSS-460/470" sometime later to day.

Regards,
Joe
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germaniac



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PostPosted: Wed Jul 11, 2007 4:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

A schemo pic of the LFO/BBD section is now posted over on the circuit-bending forum.

Regards,
Joe
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v-un-v
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PostPosted: Thu Jul 12, 2007 6:56 am    Post subject: Reply with quote  Mark this post and the followings unread

I've got a Casio VA-10 which has got a totally wild programmable FX circuit built in. I've never opened it- as I don't want to destroy it. It's lovely.
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